Background and Objective: These studies are targeted towards understanding the pathogenesis of psoriatic arthritis and the development of specific immunotherapies for psoriatic arthritis, a relatively common chronic inflammatory disease affecting the skin and joints. Patients with known or suspected psoriatic arthritis are evaluated at the Clinical Center. Studies include characterization of the clinical and laboratory features of the disease, research studies of the natural history, pathogenesis and determination of the patients' eligibility to enter experimental therapeutic protocols. Results: Recruitment in this study was slow over the last year primarily because the beneficial effect and wide availability of new TNF-inhibitors in the community. Conclusion and Significance: This study allows us to recruit patients for treatment protocols, provide second opinions for patients with difficult to treat disease and to further explore the pathogenesis of psoriatic arthritis. Lay Summary. Psoriasis is a common inflammatory disease of the skin that affects approximately 2% of the population of the USA. Psoriasis is accompanied by a destructive arthritis in 5-15% of patients. Our studies examine the relative contribution of certain types of blood cells and their products in causing this disease. Thus far we have established an important role of certain blood cells called T lymphocytes and monocytes in causing inflammation. In addition, we have identified several molecules produced by these cells that cause inflammation which could be targets for future therapy. Progress since last year 1. We submitted for publication the results of a therapeutic protocol using fludarabine in patients with psoriatic arthritis. 2. We participated in the design of a therapeutic protocol with an anti-CD2 monoclonal antibody; however, this project was on hold by the company supplying the drug Goals for next year 1) Development of new treatment protocols for patients with psoriatic arthritis